In the charging of coke ovens with crushed coal, larry cars move upon the top of the coke ovens to position batch-type hoppers over charging holes through which coal is charged. Such hoppers are usually gravity operated, although a discharging device, such as a screw-feed or table-feed mechanism can be used.
During the charging operation, the larry car operator must be able to detect when hoppers are empty in order to quickly close the hopper discharge opening of each hopper, to prevent escape of charging emissions, and also to prevent damage to the hopper interior from any hot gases which may escape from the coke oven. In order to avoid the need for such operators to leave their air conditioned cabs to detect when hoppers are empty, a reliable indicating device is needed. Such device must be capable of automatically indicating when hoppers are empty, be of rugged construction and designed so that the device itself does not contribute to or cause arching or hang-up of material within the hopper. In addition, it would be desirable for such device to automatically close the discharge opening of the hopper, as soon as the hopper is empty.